The present invention provides a process for the polymerization of fluorinated olefin monomers using fluoroxy compund solutions as initiators.
U.S. Pat. No. 2,559,630 (Bullitt) discloses the polymerization of fluoroolefins, including tetrafluoroethylene (TFE), initiated by a fluorinated acyl peroxide of the formula ##STR1## wherein X is H or F and n is at least 2.
E.P.O. App. 0,093,404 (Daikin) discloses the copolymerization of TFE with fluoroalkylvinyl ethers in liquid medium, initiated by a fluorinated acyl peroxide of the formula ##STR2## wherein n is 1 to 10.
Porter et al., J. Am. Chem. Soc., 79, 5625 (1957) disclose the use of trifluoromethyl hypofluorite, CF.sub.3 OF, to initiate gas-phase polymerization of TFE at room temperature.
Acyl hypofluorites of less than five carbon atoms have previously been reported. Cady et al., J. Am. Chem. Soc., 75, 2501 (1953), disclose the preparation of trifluoroacetyl hypofluorite (CF.sub.3 CO.sub.2 F) in low yield by fluorination of trifluoroacetic acid. Menefee et al., J. Am. Chem. Soc., 76, 2020 to 2021 (1954), disclose the preparation of pentafluoropropionyl hypofluorite, C.sub.2 F.sub.5 CO.sub.2 F, and heptafluorobutyryl hypofluorite by reaction of fluorine with the corresponding acids. The authors report that by placing about 2 ml of water in the reaction vessel and removing a trap, the yield of explosive product was greatly increased.
Thompson et al., J. Am. Chem. Soc., 89, 2263 to 2267 (1967), disclose the preparation of 1,1-bis(fluoroxy)perfluoropropane and 2,2-bis(fluoroxy)perfluoropropane by direct fluorination of the monosodium salt of perfluoroacetone hydrate, (CF.sub.3).sub.2 C(OH)ONa. The authors state that, in contrast, direct fluorination of perfluoroacetone hydrate yields (CF.sub.3).sub.2 CFOF and that, in regard to the fluorination of trifluoroacetic acid and its salts, the acid affords rather low yields of the hypofluorite, CF.sub.3 C(O)OF whereas the salts give yields of up to 60% CF.sub.3 CF(OF).sub.2.
U.S. Pat. No. 3,415,865 ('865 patent), issued to Prager et al. on Dec. 10, 1968, discloses perfluoroalkyl polyfluoroxy compounds having the formula R.sub.f (OF).sub.n wherein R.sub.f is a perfluorinated alkyl radical having from 1 to 18 carbon atoms and n is an integer from 2 to 12. The disclosed compounds are stated to be useful fluorinated oxidizing agents and are prepared by direct fluorination of compounds having a molecular structure in which at least one oxygen atom is directly linked to a carbon atom. Salts of carboxylic acids are included among the starting materials and may give mixtures of monooxyfluoro- and dioxyfluoro-substituted compounds. Alkali metal salts are disclosed as suitable. The use of an inert gaseous diluent, such as N.sub.2, for fluorine is also disclosed and examples of fluorination of the sodium salts of perfluorohexanoic and perfluorodecanoic acids are given.
U.S. Pat. No. 3,420,866, issued to Prager et al. on Jan. 7, 1969, discloses the same compounds and process as the '865 patent. U.S. Pat. No. 3,442,927, issued to Thompson et al. on May 6, 1969, discloses fluoroxy compounds having the formula (R).sub.n C(F).sub.m OF wherein R is a perfluorinated alkyl radical having 1 to 18 carbon atoms, n is an integer from 1 to 3, and m equals 3n.
Barton et al., Chem. Comm. 122 to 123 (1972), discuss the behavior of several different types of fluoroxy compounds as electrophilic fluorinating agents, and state that there is some suggestion that tertiary fluoroxy compounds might be disposed to free radical reactions.
Rozen et al., Tetrahedron Lett., 725 to 728 (1979), report that an oxidative solution results when elemental fluorine is passed into a suspension of CF.sub.3 COONa in "freon" at -75.degree. C., and that up to 50% of the oxidizing ability of the solution is due to the presence of CF.sub.3 CF.sub.2 OF, although all of the oxidizing compounds present are presumably of the perfluoroxyfluoride type. The authors disclose the use of this solution to effect electrophilic fluorination.
Rozen et al., J. Am. Chem. Soc., 101, 2782 to 2783 (1979), report on the fluoroxy solution mentioned in the previous paragraph and disclose that use of excess fluorine leads to bis-fluoroxy compounds. The authors state that, if CF.sub.3 COONa is not completely dried, the F.sup.- is immediately almost completely hydrated and CF.sub.3 COOF is the main reaction product. Use of CF.sub.3 COOF as an agent to form fluorohydrins is also disclosed.
Rozen et al., J. Fluorine Chem. 16, 19 to 31 (1980), disclose the use of solutions prepared by reacting F.sub.2 with CF.sub.3 COONa in absence of H.sub.2 O as fluorinating agents to convert enol acetates to the corresponding .alpha.-fluoroketones. Rozen et al., J. Org. Chem., 45, 672 to 678 (1980), disclose the reaction of sodium trifluoroacetate with fluorine in the presence of traces of water or HF to give mainly trifluoroacetyl hypofluorite, CF.sub.3 COOF and the reaction of this in situ preparation with stilbenes and diphenylacetylene.
Lerman et al., J. Org. Chem., 46, 4629 to 4631 (1981), disclose the use of CH.sub.3 COOF as an electrophilic fluorination agent for activated aromatic rings. Lerman et al., J. Org. Chem., 48, 724 to 727 (1983), disclose the use of CH.sub.3 COOF as a fluorinating agent for 1,3-dicarbonyl derivatives.
The common initiators used for the polymerization of fluorinated olefins, such as persulfate and perfluoropropionyl peroxide, create processing problems. For example, persulfate gives products with reactive unstable end groups as evidenced by heavy discoloration of the resulting polymer during melt processing. Hydrolytic instability makes perfluoropropionyl peroxide initiation very inefficient in aqueous systems. The process of the present invention uses fluoroxy compound solutions as initiators for the polymerization of fluorinated olefins and avoids these problems, and in contrast yields polymers with few or no reactive end groups as evidenced by negligible discoloration during processing.